A gear mechanism consisting of a four-bar linkage forming a Scotch yoke performing reciprocating movements is generally known from the manuscript Getriebelehre I [Kinematics I] by Prof. Dr. B. Dizioglu, TU Braunschweig, 1974, p. 9. A drive arm that is able to rotate around a fixed bearing acts with its other end on a sliding block, which is held linearly displaceably in the guideway of a guide rail. A sliding bar, which is directed at right angles to the guideway and is guided in a fixed bearing, is fastened to the guide rail. Due to this arrangement, transformation of a rotary movement of the drive arm into a longitudinal movement of the guide rail at right angles to its guideway and to the sliding bar fastened to it is achieved. Thus, the guide rail and the sliding bar are arranged in a cross-shaped pattern. During clockwise rotation of the drive arm out of a position that is parallel to the sliding bar through 180.degree., each point of the sliding bar moves in the axial direction of the sliding bar from a front end position to a rear end position. During further rotation in the same direction, each point of the sliding bar will again move from the rear end position to the front end position, i.e., each point of the sliding bar returns from the front end position into the front end position via the rear end position during each full revolution of the drive arm. Each point of the sliding bar again moves from the rear end position to the front end position during rotation in the opposite direction as well.
The above-mentioned, well-known principle of the Scotch yoke performing reciprocating movement is applied in EP-0,339,348 A1 to the actuating mechanism of an electrical cable coupling for rail-borne vehicles. The manner of coupling and the electrical cable coupling require a separate actuation of the electrical cable coupling and of the release mechanism for the mechanical coupling for each switching cycle, so that when operating the rotary drive of the electrical cable coupling, the operator must decide on and initiate connection, i.e., coupling with the release mechanism, separately in each switching cycle if actuation of the release mechanism is necessary. The non- positive contact between the rotary drive and the cable coupling is to be abolished by arranging the last gear pair of a gear mechanism between the rotary drive and the cable coupling, which gear pair is located in the flux of force, and making it such that it is able to be disengaged.